Hyper-V exposes the VHD GUIDs to guests, which can be used to
easily identify attached disks.
This change will allow setting the VHD GUID for new as well as
existing images.
Worth mentioning that the Kubernetes Openstack provider will
benefit from this. Without it, k8s Persistent Volumes can't be
identified by some guests.
http://paste.openstack.org/raw/801011/
Change-Id: Ied73997e6f5f3ded9827703867f059ef3dfca159
cce95b44a9